1. Field of the Invention
This invention relates to electromagnetic pumps, and more particularly to electromagnetic pumps of the type that are employed to deliver oil or other liquid fuel to the burners of domestic and other furnaces and similar appliances. Pumps for this service are required to supply oil at pressures of, for example, about 100 psi at fairly low rates of flow, such as 4 to 6 gallons per hour. The pump must also have sufficient capacity to evacuate air from the oil supply line when the pump is first put into service or when the pump is placed in service again after the supply line has been drained for any reason. To meet this requirement, most United States manufacturers of oil burners require pumps that have a capacity of at least 20 gallons per hour, and in the United States most oil burners are provided with gear-type pumps that are driven directly by the same motor that drives the blower for the burner. Pumps of this type, however, are not economical in their use of electric power and may become noisy and less efficient after extended periods of use.
2. Description of the Prior Art
In order to eliminate the problems encountered with gear-type pumps in connection with oil burners, piston pumps have been provided in which the piston is driven by an armature disposed in an electromagnetic field, the arrangement being such that the piston reciprocates rapidly in its cylinder and the pump is able to pump the required low volume of oil at the desired pressure. Pumps of this type are shown in the Nakamura U.S. Pat. Nos. 3,877,840 and 3,877,841, both issued Apr. 15, 1975, and have gone into substantial use in Japan in connection with oil burners. These pumps operate satisfactorily with residential oil burners where the oil is fed by gravity from a storage tank to the pump or where the lift does not exceed about two feet, or if the lift does exceed two feet, the oil supply line does not have an outside diameter of more than about 1/4 inch and is not more than about 20 feet long. However, when such pumps are employed with systems embodying greater lift and long or larger diameter suction lines, they are unable to evacuate the air from the supply line and prime the pump because of the elasticity of the air column in the pipe and the limited pump displacement.
Pumps of this type, therefore, would be unsatisfactory for general use in United States residential and commercial heating systems, since such systems usually embody outside, below ground oil tanks with supply lines composed of 3/8 or 1/2 inch O.D. copper tubing that may be many feet in length. For this reason, pumps of the type shown in the aforesaid Nakamura patent would not be suitable for use in many United States residential and commercial heating systems. Inasmuch as the manufacturers of oil burners in the United States do not control the manner in which the burners are installed, the manufacturers must provide burners that will operate under all reasonable conditions, for this reason, electromagnetic pistontype pumps have not come into any substantial use in the oil burner industry in the United States.